Update-manager does not show all updates

Ever since I upgraded to 13.10, the software updater does not show all the available updates. Some will appear and can be installed just fine, but once it claims that all software is up to date, using sudo apt-get upgrade shows that there are still more packages waiting to be updated. I can update them via the command line, but that only solves things temporarily. I'm not sure why some show up and others don't. How can I make Update Manager update all packages?

Update-manager shows this:

But apt-get shows this:

Thanks!

This appears to be part of the phasing of stable release updates that has been in place since 13.04.

Users of Ubuntu 13.04 who install updates with update-manager are automatically participating in this process.

Basically, updates are released to 10% of users. Then an error report database looks for regressions or problems. If everything is ok, 6 hours later another 10% of users receive the updates. The phasing status tracker is automatically updated accordingly, and you can monitor the process there.

One can opt out of the Phased Update process by adding 'Update-Manager::Never-Include-Phased-Updates "True";' to the configuration file "/etc/apt/apt.conf".

On my system that file does not exist, so if you choose to opt-out, you may need to create it with sudo nano /etc/apt/apt.conf and add the needed line.

On Ubuntu releases 20.10 and earlier, apt-get will always show updates right away. In Ubuntu 21.04, phased updates came to apt-get.

Also, in System Settings >> Software and Updates, go to the Updates tab and make sure When there are security updates and When there are other updates both say Display immediately (But note that these settings do not override the phased updates.)

See also:

• Stable Release Updates on the Ubuntu Wiki, section 5: Phasing